1. Field of the Invention
The present invention relates to an inkjet printing apparatus. In particular, the present invention relates to an inkjet printing apparatus that, with use of an inkjet print head provided with a printing element substrate on which electrothermal transducing elements are arrayed, prints an image while detecting a temperature of the printing element substrate.
2. Description of the Related Art
An inkjet print head provided with electrothermal transducing elements can eject small droplets of ink at a high frequency, and a printing apparatus using such a print head can output an image at high speed and high resolution. In the inkjet print head provided with electrothermal transducing elements, a voltage pulse is applied to the electrothermal transducing elements according to an ink ejection signal. The inkjet print head is configured such that, by doing so, film boiling occurs in ink in contact with the electrothermal transducing elements, and by growth energy of generated bubbles, ink droplets are ejected from ejection ports (nozzles).
In such an inkjet print head, temperature of a printing element substrate on which the plurality of electrothermal transducing elements are arrayed is changed depending on the number of times of driving, i.e., the number of times of ejection of each of the electrothermal transducing elements. Also, a size of forming bubble, i.e., an amount of ink ejected from an ejection port (ejection amount) in a corresponding electrothermal transducing element depends on the temperature of the printing element substrate. On the other hand, the ejection amount is also changed by the pulse shape of the voltage pulse applied to the electrothermal transducing element. From the above, in many of inkjet printing apparatuses each of which is mounted with an inkjet print head provided with electrothermal transducing elements, a pulse shape to be applied to the electrothermal transducing elements is adjusted depending on a detected temperature of a printing element substrate to keep a stable ejection amount independently of the temperature of the printing element substrate.
Meanwhile, in an inkjet printing apparatus of recent years, along with an increase in length of a print head, an increase in the number of nozzle arrays, and further an increase in size of a printing medium toward A3 or A2 sizes, a temperature rise during one scan of the print head has become marked. For this reason, it has been required to, during the scan of the print head, perform feedback control that detects a temperature of the print head, and on the basis of the detected temperature, modulates a voltage pulse to be applied to electrothermal transducing elements. In this case, an output signal of a temperature sensor is an analog signal, and a wing line for the signal is arranged on a printing element substrate with being in close contact with other wing line for driving signals for the electrothermal transducing elements and logic signals for controlling ink ejection nozzles and ejection timing. Also, the analog signal is transmitted to a main board of a main body through a flexible cable that is bent along with the scan of the print head. From the above, on the output signal of the temperature sensor, which is transmitted during the print scan, noise due to interference with the other signals is inevitably superimposed.
For example, Japanese Patent Laid-Open No. H06-297718 (1994) discloses a method that, from a print duty (print density) per unit time, estimates a temperature rise of a print head, and adds the estimated temperature rise to a detected temperature before ejection to determine a pulse shape of a driving signal. Also, Japanese Patent Laid-Open No. 2002-264305 discloses a method that, in accordance with timing when driving signals to all electrothermal transducing elements on a printing element substrate are in a disable (OFF) state, monitors a temperature sensor on the printing element substrate. According to the method in Japanese Patent Laid-Open No. H06-297718 (1994) or Japanese Patent Laid-Open No. 2002-264305, during ejection of the print head, i.e., during transmission of the driving signal, a temperature detection signal is not detected or transmitted, and therefore noise due to interference with the other signals is not provided to a temperature sensor output signal, and therefore a highly reliable head temperature can be obtained.
Meanwhile, in the method of Japanese Patent Laid-Open No. H06-297718 (1994), in order to estimate the temperature rise of the print head, it is necessary to temporarily store the print duty per unit time. In this case, in a recent print head configuration that is long-sized and provided with a number of nozzle arrays, a large-capacity memory is required, and a capacity of a main body memory of a printing apparatus may be made tight.
Also, as in Japanese Patent Laid-Open No. 2002-264305, even in the case of attempting to use the timing when the driving signals are in the disable (OFF) state, in a situation where an ejection operation is performed by the plurality of nozzle arrays at a high frequency, ensuring itself of the timing of the disable state is difficult. In particular, in a situation where further increases in speed and resolution are required, an ejection frequency of the print head is increased to cause a drastic temperature rise, and therefore the monitoring of the temperature sensor is more frequently required. However, on the other hand, the timing of the disable state is also increasingly reduced in duration, and therefore performance itself of the method in Japanese Patent Laid-Open No. 2002-264305 becomes difficult.
On the other hand, even in the configuration adapted to detect and transmit the temperature detection signal during transmission of the driving signal, a method that increases the number of times of samplings per unit time to suppress noise by a moving average process is possible. However, in this case, obtained head temperature has a problem of being unable to follow a temperature change along with a drastic change in the number of times of simultaneous driving.